Every time a player's contract has to be renewed, there will be an asking bonus, and the wage will probably increase. You will probably pay more if you renew a player's contract every year rather than only in the final year of the contract or just after expiry. Also, it is probably better to renew the contract on the first few days of the season if you are sure you intend to keep the player for at least the current season and a good part of next season.